The invention relates to a process for degreasing, cleaning, deoxidizing, etching and/or activating surfaces of solid objects that are constructed of and/or coated with metallic aluminum and/or aluminum alloys that contain at least 55 atomic percent of aluminum and that may be soiled with a wide variety of contaminants when the process is begun. Hereinafter, unless the context requires otherwise to be sensible or there is an express contrary indication, such as the use of the qualifier xe2x80x9cpurexe2x80x9d or the like, the term xe2x80x9caluminumxe2x80x9d when used to describe a substrate being treated by or suitable to be treated by a process according to this invention is to be understood to include pure aluminum and all the alloys of aluminum that contain at least 55 atomic % of pure aluminum. Preferred aqueous compositions and processes of the invention provide satisfactory preparation of dean electrochemically active aluminum surfaces for use in subsequent surface finishing operations in the aerospace industry and in many other industrial uses of aluminum.
Aluminum articles in contact with the ambient natural atmosphere spontaneously develop surface layers, largely constituted of aluminum and oxygen atoms, that cause the aluminum surfaces to become electrochemically xe2x80x9cpassivexe2x80x9d, i.e., not to undergo at any readily appreciable rate many electrochemical reactions, such as the displacement plating of copper onto the aluminum surface when it is contacted with an aqueous liquid that contains copper cations in solution, that would be expected, from thermodynamic electrode potentials for metallic aluminum, to occur readily. Before many of the surface treatment processes desired to be used on aluminum articles can be effectively undertaken, much or all of this passivating layer must be removed from any aluminum surface that has it. Removing such layers is known in the art as a xe2x80x9cdeoxidizingxe2x80x9d or xe2x80x9cetchingxe2x80x9d process, these terms being intended to be interchangeable herein.1 
1In principle, xe2x80x9cetchingxe2x80x9d requires continuing appreciable dissolution of the surface being etched during prolonged exposure of the same aluminum surface to an etching process, while xe2x80x9cdeoxidizingxe2x80x9d could occur without such continuing dissolution, by removing only the portions of the surface initially constituted of oxides and other non-elemental forms of the underlying metal, or by transforming these portions into elemental metal or alloy, without the necessity of dissolving any of the substrate that was originally in elemental form. In practice, however, no such xe2x80x9cidealxe2x80x9d deoxidizing process has ever been developed, so that achieving deoxidizing also 
requires etching, and the two terms are usually used interchangeably.) 
Also, many mechanical operations such as stamping, cutting, welding, grinding, drawing, machining, and polishing are used in the aluminum industry to provide shaped metal articles. In metal working operations, lubricants, antibinding agents, machining coolants and/or the like are normally utilized to prevent binding and sticking of the tools to the metal articles in the various metal working operations. The lubricants, coolants, and antibinding agents and/or the additives present in these compositions usually leave an oily, greasy, and/or waxy residue on the surface of the metal which has been worked. Any such residue initially present normally should be removed before a worked article is given a protective surface finish or incorporated into a finished assembly. Processes of this type are known as xe2x80x9cdegreasingxe2x80x9d and/or xe2x80x9ccleaningxe2x80x9d, with the latter of these terms being somewhat more general, because it requires removal of all contaminant materials, with a possible exception for tightly adhering conversion coatings such as the passivating oxide layers on aluminum.
At present, it is usually practically necessary to provide distinct types of treatment compositions and processing conditions to accomplish degreasing/cleaning and deoxidizing/etching. This necessity increases the cost of processing. Accordingly, a major object of this invention is to provide compositions and processes that will practically accomplish degreasing/cleaning and deoxidizing/etching simultaneously, a combination of utilities generally denoted hereinafter as xe2x80x9ccleaning/deoxidizingxe2x80x9d, so that aluminum articles having greasy or otherwise soiled and at least partially passivated surfaces are made ready simultaneously for further surface treatment(s), usually including formation of a conversion coating, that enable the articles to meet the highly demanding standards of the aerospace industry, along with those of any or almost any other practical use of aluminum. Other objects will be apparent from the description below.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word xe2x80x9caboutxe2x80x9d in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, xe2x80x9cparts ofxe2x80x9d and ratio values are by weight or mass; the term xe2x80x9cpolymerxe2x80x9d includes xe2x80x9coligomerxe2x80x9d, xe2x80x9ccopolymerxe2x80x9d, xe2x80x9cterpolymerxe2x80x9d and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word xe2x80x9cmolexe2x80x9d means xe2x80x9cgram molexe2x80x9d, and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; and the terms xe2x80x9csolutionxe2x80x9d, xe2x80x9csolublexe2x80x9d, xe2x80x9chomogeneousxe2x80x9d, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18-25xc2x0 C.
It has been found that at least the major object of the invention as stated above can be achieved by use of a liquid working composition combining water and at least one of glycol, xe2x80x9cpolyglycolxe2x80x9d2, and glycol and polyglycol ether molecules as its two major constituents and also including alkalinizing agents and surfactant molecules, and, optionally and preferably, fluoride anions and/or chelating agents for multivalent metal cations (i.e., metal cations with at least two positive electric charges). More specifically, a working composition, i.e., a composition ready for use as such in cleaning/deoxidizing according to the invention, comprises, preferably consists essentially of, or more preferably consists of, water and the following dissolved components:
2As is generally known in the art, these are condensation polymers, in which one molecule of water has been eliminated for each except the first of the glycol xe2x80x9cmonomersxe2x80x9d in the polymer, resulting in an ether oxygen bond between each two carbon chains characteristic of the glycol monomers from which the polyglycol is at least formally derived. 
(A) a component of organic molecules of compounds that are liquid at 25xc2x0 C. and are selected from the group consisting of: compounds made up of molecules that contain at least one, preferably at least two, hydroxyl oxygen atoms and otherwise contain only carbon and hydrogen and, optionally, halogen atoms, or preferably only carbon and hydrogen atoms; and compounds made up of molecules that contain at least one, or preferably at least two, ether oxygen atom(s) and otherwise contain only carbon, hydrogen, hydroxyl oxygen, and/or halogen atoms, or preferably only carbon and hydrogen atoms and, optionally, not more than one hydroxyl oxygen atom;
(B) a component of alkalinizing agent, often alternatively known in the detergent art as xe2x80x9cbuilderxe2x80x9d, exclusive of any that contain fluoride anions; and
(C) a component of alkali stable surfactant molecules that are not part of any of immediately previously recited components (A) and (B); and, optionally, one or more of the following components:
(D) a component of fluoride anions; and
(E) a component of chelating agents that are not part of any of immediately previously recited components (A) through (D); and
(F) a component of hydrotroping agent that is not part of any of immediately previously recited components (A) through (E).
In this description,xe2x80x9calkali stablexe2x80x9d when referring to a surfactant means that the surfactant is capable of coexisting at its critical micelle concentration or at a concentration of 5% in an aqueous solution also containing at least, with increasing preference in the order given, 5, 10, 15, 20, 25, or 29% of sodium hydroxide, without any chemical reaction (except possibly for reversible neutralization) between the surfactant and the sodium hydroxide and without the formation of any separate bulk phase detectable with normal unaided human vision within 24 hours, or preferably, with increasing preference in the order given, within 7, 30, 60, 90, 120, 180, 240, 300, or 360 days, of storage without mechanical agitation at 25xc2x0 C. after being initially mixed.
In addition to the working compositions described above, embodiments of the invention include: concentrate compositions suitable for preparing working compositions by mixing the concentrate composition with water and, optionally, other concentrate compositions; replenisher compositions, suitable for maintaining the cleaning/deoxidizing effectiveness of a selected quantity of a working composition according to the invention by restoring to it any ingredients of the selected quantity of working composition that are removed from the quantity of working composition during its use and are needed to maintain its effectiveness; and process embodiments, which include at a minimum contacting an aluminum article substrate with a working composition according to the invention to remove any soils initially present on the substrate and produce a surface that is free from any water breaks when contacted with pure liquid water and that will spontaneously plate itself with copper within a time of ten minutes from its immersion at 25xc2x0 C. in an aqueous solution of copper(II) sulfate containing at least 1% of copper(II) cations, and may include other process steps, particularly those which are conventional in themselves preceding or following etching/deoxidizing and/or cleaning/degreasing aluminum surfaces in the prior art.
In addition to the above noted necessary and optional materials, compositions of the present invention can additionally contain germicides, preserving agents and the like, and they can, and after a period of use usually do, contain very substantial amounts of dissolved aluminum, mostly in the form of aluminate anions. A composition of the present invention does not generally require the presence of a foam suppressing agent. The inclusion of foam suppressing agents, however, is also within the broad scope of the invention.
Working compositions and processes according to this invention are effective over a wide range of pH values. For primary degreasing/deoxidizing prior to most subsequent operations, an alkaline working composition according to the invention is preferred because it generally effects adequate degreasing more rapidly. The particular degree of alkalinity that is most preferred generally requires a compromise between quick degreasing, which is favored by greater alkalinity, and avoiding excessive corrosion, which is favored by lower alkalinity. The alkalinity is conveniently measured for preparation of a working composition according to the invention and for replenishment during use of such a composition by a value denoted as xe2x80x9cfree causticxe2x80x9d with units of grams per liter, hereinafter usually abbreviated as xe2x80x9cg/lxe2x80x9d, and measured by the following test:
A sample of the liquid composition in which there is dissolved aluminum and in which free caustic is to be measured is filtered, using a Buchner funnel, vacuum filtration flask, and Whatman #50 hardened filter paper. A 10.0 milliliter (hereinafter usually abbreviated as xe2x80x9cmlxe2x80x9d) aliquot of the filtered composition, about 30 ml of hot distilled, deionized, or similarly pure water (hereinafter usually abbreviated as xe2x80x9cDI waterxe2x80x9d), and about 10 ml of a solution of barium chloride in water that contains 100 g/l of BaCl2 are mixed in succession in a container such as a beaker, causing precipitation of any non-hydroxide alkalinizing agent content of the liquid composition as barium salt(s). The mixture of liquid and precipitate is filtered, using the same type of filtration equipment as before except that a glass fiber filter having a pore size of 1.2 micrometres (hereinafter usually abbreviated as xe2x80x9cxcexcmxe2x80x9d) is used instead of filter paper. The container is rinsed twice with a volume of 30 to 50 ml of DI water each time, with the rinse water being filtered through the same filter as, and collected with the filtrate from, the first filtration after addition of the BaCl2 solution.
The remnant water in the container is then tested with pH paper, which should indicate a neutral pH; if it does not, additional rinsing with DI water should be continued until the remnant water does have a neutral pH, using as small a volume of additional rinse water as possible to accomplish this purpose.
After all rinsing is completed, the filtration should be continued until the filtered precipitate is dry and no further drops of liquid are observed to pass through the funnel. The filtrate liquid is then titrated with 1.00 N HCl solution to a white turbid endpoint (precipitation of hydrous aluminum oxide as the pH of the liquid phase falls). The value of free caustic in g/l is 5.6 times the number of ml of 1.00 N acid solution consumed in the titration.
If it is also desired to determine the dissolved aluminum content in the original composition, 4 drops of phenolphthalein indicator solution are added to the titration mixture at this point, and the titration is continued until the pink color disappears. The number of additional ml of 1.00 N acid required to reach this second end point, multiplied by 2.67, yields the value of g/l of dissolved aluminum in the original composition.
If the composition does not contain aluminum, the free caustic is determined in the same way, except that phenolphthalein indicator solution is added to the filtrate immediately, and the titration is to disappearance of the pink color; no precipitate should form during this titration.
For these aerospace industry applications of the invention when rapid cleaning/deoxidizing is desired, specifically when a layer 5 xcexcm deep inward from the surface must be removed from the substrate during not more than 15 minutes of contact time between the substrate surface and the cleaning/deoxidizing liquid composition, but the total depth of material removed during a complete cleaning/deoxidizing process on a given substrate article may not exceed 5 Mm, the free caustic value of a working composition according to the invention preferably is at least, with increasing preference in the order given, 2, 4, 6, 8, 10, 12, or 14 g/l and independently preferably is, with increasing preference in the order given, not more than 120, 100, 80, or 60 g/l and, unless exceptionally fast etch rates are desired, more preferably is not more than, with increasing preference in the order given, 55, 50, 45, 40, 35, or 30 g/l. Lower values within these preferences are normally preferred when the content of dissolved aluminum in the composition is relatively low and higher values are normally preferred when the content of dissolved aluminum in the composition is relatively high, in order to maintain a constant etch rate as part of a cleaning/deoxidizing process according to the invention.
Component (A) is preferably selected from molecules each of which contains at least two ether oxygen atoms and one hydroxyl oxygen atom and otherwise contains only carbon and hydrogen atoms, and, optionally, halogen atoms; more preferably, primarily for reasons of economy, these molecules contain no halogen atoms. Independently, component (A) is preferably selected from molecules each of which contains at least, with increasing preference in the order given, 2, 4, 6, or 8 carbon atoms and independently preferably contains not more than, with increasing preference in the order given, 18, 16, 14, or 10 carbon atoms. Independently of all other preferences, component (A) further is selected from substances that are sufficiently soluble in water to form a solution containing at least, with increasing preference in the order given, 2, 5, 10, 12, 15, 18, or 20% of the substance(s) selected for component (A). The single most preferred material for component (A) is one generally known as xe2x80x9cdiethylene glycol monobutyl etherxe2x80x9d, which has the chemical formula HOxe2x80x94C2H4xe2x80x94Oxe2x80x94C2H4xe2x80x94Oxe2x80x94C4H9. Independently of its exact chemical constitution, component (A) in a working composition according to the invention preferably is present in a concentration of at least, with increasing preference in the order given, 2, 5, 10, 12, 15, 17, 18.0, 19.0, 19.5, or 19.9% and independently preferably, primarily for reasons of economy, is not more than, with increasing preference in the order given, 75, 50, 40, 35, 30, 27, 25, 23, or 21%.
Alkalinizing component (B) is preferably selected from various inorganic salts and hydroxides known to be useful as xe2x80x9cinorganic buildersxe2x80x9d in cleaning formulations generally. Inorganic builders, except for hydroxides, are generally salts of polyfunctional inorganic acids, such as alkali metal silicates, alkali metal borates, alkali metal carbonates, alkali metal sulfates, alkali metal polyphosphates, alkali metal phosphates, alkali metal orthophosphates, and alkali metal pyrophosphates. Salts such as sodium silicate, sodium metasilicate, sodium orthosilicate, sodium tetraborate, sodium borate, sodium sulfate, sodium carbonate, trisodium phosphate, disodium orthophosphate, sodium metaphosphate, sodium pyrophosphate, the corresponding potassium salts to all of these, sodium and potassium hydroxides, and the like are all suitable alkalinizing agents for compositions according to the present invention. Lithium, rubidium, and cesium salts and hydroxides are also suitable, although usually less preferred because of their higher cost, and ammonium salts are technically suitable but are generally avoided because of the chance of loss by volatilization and the accompanying odor nuisance of ammonia fumes. Because of higher solubility, potassium cations are preferred over sodium cations in most instances in constituents of alkalinizing component (B), despite their slightly higher cost.
More preferably, in a composition according to this invention, an alkali metal hydroxide and an alkali metal salt of a polyfunctional inorganic acid are both part of component (B). More particularly, a freshly prepared working composition according to the invention, free of dissolved aluminum, preferably contains hydroxide ions in a concentration that is at least, with increasing preference in the order given, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, or 0.43% of the total composition and independently preferably is not more than, with increasing preference in the order given, 3.0, 2.5, 2.0, 1.5, 1.0, 0.80, 0.70, 0.65, 0.60, 0.55, 0.50, or 0.45% of the total composition. (The concentrations specified as preferable in this paragraph are to be understood to include the entire stoichiometric equivalent as OHxe2x88x92 of all soluble hydroxides added in the course of preparation of a composition according to the invention, unless some of this content has been removed by physical means.)
The free caustic value determined as described above is the strongest compositional influence on the etch rate obtained with a composition according to the invention, the etch rate increasing with increasing free caustic value. The free caustic value in a freshly prepared preferred composition according to the invention is nearly equivalent to the concentration, expressed in g/l, of the stoichiometric equivalent as KOH of the hydroxide ion concentration in the same composition, but as the composition is used, much of its originally added hydroxide ions content is converted to aluminate anions, which do not contribute any substantial amount to the free caustic value.
Independently, a composition according to the invention that contains both hydroxide and non-hydroxide materials for component (B) preferably contains the nonhydroxide materials, which are independently preferably selected from the group consisting of fully neutralized salts of polyfunctional inorganic acids, in a concentration that is at least, with increasing preference in the order given, 0.010, 0.020, 0.030, 0.040, 0.050, 0.055, 0.060, 0.065, or 0.070 moles of non-hydroxide alkalinizing agents per kilogram of total composition, this concentration unit being freely applied hereinafter to any other solute as well as to non-hydroxide alkalinizing agents and being hereinafter usually abbreviated as xe2x80x9cM/kgxe2x80x9d. The concentration of non-hydroxide alkalinizing agents independently preferably is not more than, with increasing preference in the order given, 0.50, 0.40, 0.30, 0.20, 0.17, 0.14, 0.12, 0.10, or 0.08 M/kg. Carbonates are the single most preferred non-hydroxide alkalinizing agents in a composition according to the invention, inasmuch as they normally can be replenished, to the slight extent that their replenishment is needed, by absorption of carbon dioxide from the natural ambient atmosphere.
Component (C) preferably contains two subcomponents. Preferred subcomponent (C.1) is selected from the group consisting of Alkali Surfactant JEN 2700(trademark), commercially supplied by Tomah Chemical Products, Milton, Wisconsin and reported by its supplier to be a solution in water of about 35% of its surfactant ingredient, monosodium salt of iso-decyloxypropylaminodipropionic acid, an amphoteric surfactant, and SURMAX(trademark) CS504, xe2x88x92515, xe2x88x92521, xe2x88x92522, xe2x88x92555, xe2x88x92586, xe2x88x92634, xe2x88x92684, xe2x88x92727, xe2x88x92772, and xe2x88x92786 surfactans, all commercially available from Chemax, Inc., Greenville, S.C. and reported by their supplier to be amphoteric-anionic alkali stable surfactants that include organic esters, and/or salts of organic esters, of phosphoric acid, with other compositional information being proprietary. The concentration of subcomponent (C.1) in a composition according to the invention preferably is at least, with increasing preference in the order given, 0.02, 0.04, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, or 0.20% of the total composition and independently preferably is not more than, with increasing preference in the order given, 1.0, 0.90, 0.80, 0.70, 0.60, 0.50, 0.40, 0.35, 0.30, or 0.25% of the total composition.
Preferred subcomponent (C.2) is selected from the group consisting of ethoxylates of alkyl phenols, more preferably octyl and nonyl phenols, these ethoxylates independently preferably having a hydrophile-lipophile balance (hereinafter usually abbreviated as xe2x80x9cHLBxe2x80x9d) value that is at least, with increasing preference in the order given, 9.0, 10.0, 11.0, 12.0, 12.5, 13.0, or 13.4 and independently preferably is not more than, with increasing preference in the order given, 16.0, 15.0, 14.5, 14.1, 13.8, or 13.6. Independently, the concentration of subcomponent (C.2) in a composition according to the invention preferably is at least, with increasing preference in the order given, 0.05, 0.10, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, or 0.48% of the total composition and independently preferably is not more than, with increasing preference in the order given, 3.0, 2.5, 2.0, 1.5, 1.2, 0.90, 0.70, 0.60, or 0.52% of the total composition.
When subcomponents (C.1) and (C.2) as defined above are both present in a composition according to the invention, the ratio of the concentrations, expressed in the same units, of subcomponents (C.1) and (C.2) in the composition preferably is at least, with increasing preference in the order given, 0.10:1.0, 0.15:1.0, 0.20:1.0, 0.25:1.0, 0.30:1.0, 0.35:1.0, or 0.40:1.0 and independently preferably is not more than, with increasing preference in the order given, 1.0:1.0, 0.80:1.0, 0.70:1.0, 0.60:1.0, 0.55:1.0, or 0.50:1.0.
The presence of optional component (D) of fluoride anions in a working composition according to the invention is normally preferred, because it favors a uniform surface appearance at the completion of a cleaning/deoxidizing process according to the invention. However, if this is not important in a particular application, component (D) may be omitted. Fluoride ions may be provided to a composition according to the invention by any of the sufficiently water soluble salts and acids that contain either simple or complex fluoride anions and when thus supplied are presumed, for purposes of calculations of fluoride anions content of the composition, to be present to the full stoichiometric extent of fluorine-atom-containing anions in the materials dissolved in the composition, irrespective of the actual extent of ionization that may exist in the composition. Primarily for reasons of economy, sources of simple fluoride anions are generally preferred, and because of the high alkalinity preferred for the composition as a whole, salts are preferred over acids as the source of the fluoride anions. The same counterions in these salts as described above for the alkalinizing component (B) are preferred for component (D) for the same reasons. Potassium fluoride is the single most preferred source for component (D).
In a freshly prepared or otherwise dissolved-aluminum-free working composition according to the invention, the concentration of fluorine in the form of fluoride anions preferably is at least 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, or 0.16 parts per thousand parts of the total composition, a unit of concentration that may be freely applied herein-after to any other constituent of the composition as well as to fluorine and is usually abbreviated as xe2x80x9cpptxe2x80x9d, and independently preferably is not more than 1.0, 0.80, 0.60, 0.40, 0.35, 0.30, 0.25, or 0.20 ppt.
Because fluoride anions are at least moderately effective complexing agents for aluminum(III) cations, converting them partially to hexafluoroaluminate(III) anions, after composition according to the invention has been in use or for some other reason contains a substantial amount of dissolved aluminum, the fluoride content of the composition is preferably controlled by a measurement called xe2x80x9cfree fluoridexe2x80x9d rather than by the total fluorine content of the composition. xe2x80x9cFree fluoridexe2x80x9d is measured by use of an ionspecific electrode and associated equipment known to those skilled in the art. The free fluoride value of a freshly prepared composition according to the invention preferably should be measured and used as a target for fluoride additions, when such additions are needed as the composition is used, to restore the original free fluoride value for the freshly prepared composition.
Optional chelating agent component (E) is usually preferred in most compositions according to the invention. Any material recognized in the art as a chelating agent for aluminum, calcium, and/or magnesium cations in aqueous solution may be used. The exact function of the chelating agent is not known, but it has at least two potentially valuable functions: As a chelating agent for aluminum, it can promote the etching rate of a composition containing it, and as a chelating agent for calcium and magnesium, it can make the use of tap water instead of DI water satisfactory in some instances.
Preferred chelating agents include sufficiently water-soluble organic compounds, and the metal salts of such of these compounds as are organic acids, that contain at least two xe2x80x94OH moieties (which may or may not be part of carboxyl moieties) positioned within the molecules of the compounds in such a way that the two oxygen atoms are separated from each other by at least two carbon atoms. Examples of such organic compounds include nitrilotriacetic acid (xe2x80x9cNTAxe2x80x9d), ethylene diamine tetraacetic acid (xe2x80x9cEDTAxe2x80x9d), citric, tartaric, malic and gluconic acids and their salts, and saccharides (sugars), with the latter preferred and sorbitol particularly preferred. Independently of its exact chemical constitution, the concentration of the chelating agent component in a working composition according to the invention preferably is at least, with increasing preference in the order given, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, or 0.14% of the total composition and independently preferably is not more than, with increasing preference in the order given, 1.0, 0.8, 0.6, 0.40, 0.35, 0.30, 0.25, 0.20, or 0.15% of the total composition.
Optional hydrotroping component (F) is not generally needed in most working compositions according to this invention, in part because many of the preferred constituents of component (C) have some hydrotroping effect, but is useful in a preferred replenisher composition as noted further below. Conventional hydrotroping agents such as the salts of alkyl benzene sulfonic acids, particularly of cumene sulfonic acid, are suitable for compositions to accomplish the cleaning purposes of this invention, but may interfere with the later intended use of the substrates to be cleaned, because very low tolerances for residual sulfur on the surface are specified for many aerospace applications. Other types of hydrotropes are therefore preferred, when an additional hydrotrope is needed, for most formulations according to this invention. Organic phosphate esters and alkyl and alkenyl substituted cyclic acid anhydrides, particularly the anhydrides of C4-6 terminal dicarboxylic acids substituted with alkyl or alkenyl groups having 6 to 20 carbon atoms are both useful. A particularly preferred example of this type of hydrotrope is nonenyl succinic anhydride. These two types are even more preferred in combination with each other, in a ratio of phosphate esters to substituted cyclic anhydrides that preferably is, with increasing preference in the order given, at least 0.1, 0.2, 0.4, 0.6, 0.80, 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, or 1.55 and independently preferably is, with increasing preference in the order given, not more than 20, 15, 10, 7, 5, 4, 3, 2.7, 2.4, 2.2, 2.0, 1.9, 1.8, 1.75, 1.70, or 1.65. A particular commercial hydrotroping agent, AMPHOTERIC SC from Tomah Products, Inc., with a chemical constitution unknown to the applicant except that its active ingredients are xe2x80x9cbased on alkyliminodipropionatesxe2x80x9d and constitute 35% of the total composition as commercially supplied (the balance presumably being water) has also been found to be effective and is most preferred. The amount of hydrotroping agent is not believed to be critical, but should be sufficient to accomplish its purpose and, for reasons of economy, preferably is little or no more than this sufficient value. As a general guide, the amount of hydrotroping agent in a principal replenisher composition according to the invention that includes at least 7% of potassium hydroxide and at least 0.1% of nonionic surfactants preferably is at least, with increasing preference in the order given, 0.1, 0.3, 0.5, 0.7, or 0.9% and independently preferably is not more than, with increasing preference in the order given, 11, 7, 5, 3, 2.0, or 1.1%.
As would be expected in view of some of the discussion above, the ingredients of a composition according to the invention are not depleted during use in the same proportions as they are present in a preferred freshly made working composition according to the invention. It has been found that two replenishers are preferred, one containing only fluoride anions and their counterions as active ingredients, and another that contains all of the other ingredients of a preferred working composition according to the invention, except the non-hydroxide alkalinizing agent if the latter is a carbonate salt as is most preferred, plus a hydrotroping agent, but with considerably greater concentrations of component (B) and smaller concentrations of the other necessary components and of the optional but preferred chelating agents. More particularly, a principal replenisher composition according to the invention is a liquid that in addition to water preferably comprises, more preferably consists essentially of, or still more preferably consists of the following concentrations of the components already defined by letter identifiers for working compositions:
component (A) preferably is present in a concentration of at least, with increasing preference in the order given, 0.44, 1.1, 2.2, 2.6, 3.3, 3.7, 4.0, 4.10, 4.20, or 4.30% and independently preferably, primarily for reasons of economy, is not more than, with increasing preference in the order given, 17, 11, 8.8, 7.7, 6.6, 6.0, 5.5, 5.0, or 4.5%;
hydroxide ions are preferably present in a concentration that is at least, with increasing preference in the order given, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or 4.3% of the total composition and independently preferably is not more than, with increasing preference in the order given, 30, 25, 20, 15, 10, 8.0, 7.0, 6.5, 6.0, 5.5, 5.0, or 4.5% of the total composition;
subcomponent (C.1) is preferably present in a concentration that is at least, with increasing preference in the order given, 0.05, 0.009, 0.019, 0.023, 0.030, 0.033, 0.037, 0.042, or 0.047% of the total composition and independently preferably is not more than, with increasing preference in the order given, 0.23, 0.21, 0.19, 0.16, 0.14, 0.12, 0.093, 0.081, 0.069, or 0.058% of the total composition;
subcomponent (C.2) is preferably present in a concentration that is at least, with increasing preference in the order given, 0.02, 0.04, 0.07, 0.090, 0.095, 0.100, 0.105, or 0.110% of the total composition and independently preferably is not more than, with increasing preference in the order given, 1.1, 0.9, 0.7, 0.50, 0.35, 0.23, 0.18, 0.14, or 0.12% of the total composition;
a chelating agent component is preferably present in a concentration that preferably is at least, with increasing preference in the order given, 0.004, 0.008, 0.012, 0.016, 0.020, 0.024, or 0.028% of the total composition and independently preferably is not more than, with increasing preference in the order given, 0.20, 0.16, 0.12, 0.080, 0.070, 0.060, 0.050, 0.040, or 0.030% of the total composition.
Solid powdered potassium fluoride is effective and inexpensive and is therefore generally most preferred as the supplemental fluoride replenisher, but if a liquid replenisher should be preferred, for example because of better adaptability to automated replenishment in response to signals from a free fluoride sensing electrode, a solution in water of any of the suitable sources of fluoride can be used.
Aluminum articles to be cleaned/deoxidized should be contacted with an aqueous liquid cleaning/deoxidizing composition according to the present invention at a sufficient temperature for a sufficient time to be effective for cleaning/deoxidizing. Normally, the temperature of a working composition according to the invention during its actual use preferably is at least 32xc2x0 C. Higher etching rates will be achieved at higher temperatures, as illustrated in the examples below, and a temperature of at least 55xc2x0 C. can be satisfactorily used if a high etch rate is desired. Times of contact between the cleaning/deoxidizing composition and the substrate to be cleaned/deoxidized in a process according to the invention normally are preferably between 1 and 15 min.
The invention is particularly advantageously applied to aluminum substrates that contain at least, with increasing preference in the order given, 65, 75, 85, or 90 atomic percent of pure aluminum.